1. Field of the Invention
This invention relates to a pre-combustion chamber gas engine provided with a control valve in a communication port via which a pre-combustion chamber to which a gas fuel consisting of a natural gas from a fuel supply source is supplied and a primary chamber to which suction air is supplied communicate with each other.
2. Description of the Prior Art
An engine using a natural gas as a main fuel has heretofore been developed as an automobile engine. On the other hand, a co-generation engine has been developed to reduce urban exhaust gas emissions. In a co-generation type engine, motive power is taken out as electric energy by a generator, and water is heated with a heat exchanger by using the heat of the exhaust gas energy, to be turned to hot water, which is utilized as hot water supply. A co-generation type engine is expected to be utilized as an urban electric current supply system. An engine using a natural gas as fuel is disclosed in, for example, Japanese Patent Laid-open No. 156911/1979 and Japanese Utility Model Publication No. 41068/1991.
The internal combustion engine disclosed in Japanese Patent Laid-open No. 156911/1979 is adapted to compress suction air and supply the resultant air to a primary chamber, supply a part of the suction air to an ignition chamber, inject a hydrocarbon fuel into the ignition chamber to produce a rich mixture, further compress the air and mixture, inject the above-mentioned fuel into the primary chamber, further compress on the other hard the air and mixture to produce a lean mixture in the primary chamber, ignite the mixture in the ignition chamber before the perfect compression of the two mixtures has been attained, to produce a flow of a hot gas, and introduce this flow of a hot gas into the mixture in the primary chamber to ignite the same mixture.
The diesel engine disclosed in Japanese Utility Model Publication No. 41068/1991 is a dual fuel injection type engine provided in its cylinder head with an injection valve from which a liquid fuel is injected and an injection valve from which a gas fuel is injected. The gas fuel injection valve and a liquefied fuel gas tank in which a gas fuel is stored are connected together by two systems of gas passages, i.e. a high-pressure gas passage and a low-pressure gas passage. These gas passages are provided therein with a high-pressure compressor and a low-pressure compressor respectively for pressurizing a gas fuel to different levels of pressure and send the resultant fuel to the gas fuel injection valve. The gas fuel injection valve has a nozzle port for ejecting a high-pressure gas from the high-pressure gas passage and a nozzle port for ejecting a low-pressure gas from the low-pressure gas passage.
The fuel for a gas engine using a natural gas as fuel consists of a gas. Therefore, if an engine in which a gas fuel is burnt excellently at a high compression ratio can be manufactured, it can be operated as a gas engine using as fuel a natural gas which is said to be limitlessly obtainable.
In a gas engine, a gas fuel is sucked into a combustion chamber through a suction valve, compressed and ignited. Accordingly, the compression ratio cannot be set high, and a theoretical thermal efficiency (.eta.=thermal conversion value of work/calorific value of fuel) is not necessarily high. In a conventional gas engine, a compression ratio is around 12-13, and a theoretical thermal efficiency only 48%. When the motive power of a gas engine is converted into electric energy, the effective thermal efficiency becomes 34-35% or breaks the 30% level
Therefore, in a gas engine, 65-70% of fuel is discharged as a cooling water loss and exhaust gas energy, and, even when hot water is produced by a heat exchanger by using thermal energy and stored as hot water supply, the quantity of the hot water becomes too large, and the hot water cannot be utilized sufficiently in practice in general utility equipment. Moreover, the electric energy obtained from a gas engine costs much.
Improvement in thermal efficiency is currently expected in picking up electric energy from a gas engine. Under the circumstances, employing a heat insulating structure in a gas engine so as to improve the thermal efficiency has come to be studied. In a gas engine, a natural gas is sued as fuel, so that, when a gas sucked in a suction stroke is then compressed, high pressure and high temperature result. This causes a self-ignition phenomenon, i.e. knocking to occur. Unless the compression ratio of a gas fuel consisting of a natural gas is not higher than 12 the gas fuel is self-ignited. The thermal efficiency of an engine becomes low when the compression ratio is low. Accordingly, a gas engine has an issue as to how to set a compression ratio to a higher level while avoiding the self-ignition of a gas fuel.
In a heat insulating engine in which the temperature of the wall surface of a combustion chamber increases, a problem that the fuel supplied to the combustion chamber self-ignites before proper ignition time becomes severe. In a heat insulating engine, the temperature of the wall surface of a combustion chamber becomes as high as not lower than about 600.degree. C. Therefore, when a heat insulating engine using a natural gas or gasoline as fuel is constructed so that a compression ratio becomes high, a fuel gas and air from a suction valve are mixed and compressed at a high pressure, and self-ignition occurs, combustion starting in a position much short of a top dead center. Consequently, knocking occurs, and the engine becomes unable to be operated properly.
Therefore, constructing a gas engine as follows is thought of. A pre-combustion chamber and a primary chamber are provided, and a control valve is installed in a communication port via which the pre-combustion chamber and primary chamber communicate with each other, the pre-combustion chamber being charged with a gas fuel with suction air supplied to the primary chamber, the control valve being operated in a position in the vicinity of a compression top dead center TDC to open the communication port, mix the air and gas fuel with each other and ignite the resultant mixture. Such a gas engine poses an important issue of how to mix a gas fuel with air excellently.